1. Field of the Invention
The present invention relates to a method for preparing fatty acid esters by the reaction of fats and oils with alcohols, and a fuel comprising fatty acid esters which are prepared by such a method.
2. Prior Art
Fats and oils comprise triglycerides, that is, esters of glycerol with fatty acids, and fatty acid esters which are obtained by the transesterification of fats and oils with alcohols are widely used as industrial raw materials or medicines.
A method is reported, which produces diesel fuels or lubrication base oils containing fatty acid esters as substitutes for mineral oils by the transesterification of fats and oils with alcohols. For example, the methods disclosed in JP-A-7-197047 and JP-A-9-235573 prepare a diesel fuel by reacting waste edible oils and methanol in the presence of sodium hydroxide.
U.S. Pat. No. 5,713,965 discloses a method for the preparation of a diesel fuel and a lubricant containing fatty acid esters by the reaction of fats and oils with alcohols in hexane as a solvent in the presence of lipase.
Furthermore, a method is known, which prepares fatty acid esters by the reaction of fats and oils with alcohols while introducing a catalyst under pressure (Ullmanns Enzyklopadie der technischen Chemie, 4th Ed, Vol. 11 (1976) 432). That is, fats and oils are reacted with the 7 to 8 times excessive amount of alcohols at a temperature of 240.degree. C. under a pressure of 10 MPa in the presence of an alkali catalyst or a zinc catalyst.
However, the methods for the preparation of fatty acid esters using catalysts have some drawbacks such that the yield of fatty acid esters decreases due to the by-production of fatty acid salts, fatty acids, etc., or the process steps become complicated to remove catalysts, fatty acid salts, etc. Thus, it is highly desired to provide a simple method for the preparation of fatty acid esters at a high yield.
Hitherto, waste fats and oils are drained with no treatment, treated with coagulating agents and then discarded, burnt, or buried in ground. However, such post-treatment of waste fats and oils become the focus of public attention as one cause of environmental pollution, since the waste fats and oils are poorly decomposed under environmental conditions. Thus, a method for the preparation of a useful material containing fatty acid esters such as a diesel fuel from waste fats and oils in the absence of a catalyst is very advantageous from the viewpoint of environmental pollution, and the recover and recycle of resources.